An understanding of electrochemical dynamics at solid−liquid interfaces is essential to develop advanced batteries and fuel cells and so on. For example, an atomic-level understanding of electrochemical Pt dissolution and redeposition behavior is crucial for optimizing the material design and operating conditions of polymer electrolyte fuel cells (PEFCs). This understanding enables the prevention of the degradation of Pt nanoparticles used as electrocatalysts. However, the mechanisms of Pt dissolution and redeposition are still not fully understood due to the lack of spatial resolution available with current observation techniques. Here, we have revealed for the first time atomic-level electrochemical Pt dissolution and redeposition behavior using in-house-developed observation techniques. We achieved atomic-level observations of closed-cell type liquid electrochemical transmission electron microscopy (TEM) by combining in-housedeveloped microelectromechanical system (MEMS) chips as an electrochemical cell, an aberration-corrected TEM apparatus, and an energy filter. Furthermore, accurate and stable potential control was achieved using an in-house-developed reversible hydrogen electrode (RHE) with a liquid junction connected to the outside of a TEM specimen holder. Our observation results confirmed that Pt dissolves from surface step edges layer-by-layer, as previously predicted by the density functional theory (DFT). The observation techniques developed are also applicable to other research fields concerning electrochemistry.

A new gas injection/specimen heating holder is developed for the purpose of in situ observation of gas reaction of materials at high temperatures in a transmission electron microscope at near-atomic resolution. A fine tungsten wire is employed as a heating element of the holder and a battery is used as the power source. Gas was injected onto specimens in the form of particles lying on the heating element via a nozzle. The maximum pressure near specimens was middle of 10(-2) Pa, while the pressure in the electron-gun chamber was kept to 2 x 10(-4) Pa. This gas injection/specimen heating holder was applied to observe solid-gas reactions. The reactions observed include oxidation of pure In into In2O3, reduction of SiO2 into Si and re-oxidation of Si into SiO2.

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